The objectives are to determine the chemical compositions and structures of the lipopolysaccharide antigens of the seven immunotypes of Pseudomonas aeruginosa as classified by Fisher et al. (1969). A combination of these seven antigens has been shown effective, through stimulation of the immune response, as a vaccine for protecting human subjects against dangerous Pseudomonas infection. The chemical studies are intended to provide the basis for a rapid method for classifying Pseudomonas aeruginosa types, and to assist in developing modifications of the antigens thay may exhibit fewer undesirable side-effects while maintaining antibody-stimulating activity. Structural studies are to be conducted by specific degradative methods to furnish subunits of the lipopolysaccharides, which are then to be structurally characterized. The results should provide valuable comparative structural information on a complete range of clinically significant immunotype antigens of P. aeruginosa and offer the possibility for synthesis of artificial antigens and affinity adsorbents for isolation of homologous antibodies from hyperimmune sera.